The issues in the collection first appeared in 1990 and 1991. The collection first appeared in paperback and hardback in 1992. The title is the opening phrase of John Keats' "Ode to Autumn".
It introduces Endless siblings Destiny and Delirium, and features Thor, Odin and Loki from Norse mythology; Anubis and Bast from Egyptian mythology; Susanoo-no-mikoto from Japanese mythology; Lucifer and the Angels Duma and Remiel from Christianity; Shivering Jemmy, a Lord of Chaos with the body of a child and the mind of a monster; Kilderkin, a Lord of Order who takes the form of a cardboard box, and the fairies Cluracan and Nuala, who will play important roles in later stories. Season of Mists marks the introduction of the Norse gods for the first time in the series.
Season of Mists is the first appearance of one of the central themes of the series, that of rules and responsibilities and whether we can lay them down. The gathering of the Endless family which opens the book makes the second reference to the "prodigal", an Endless sibling who abandoned his realm and responsibilities. The family gathering leads to Dream deciding that he must return to the underworld to right a wrong he committed, an event which triggers a major plot arc throughout the series.
Morpheus leaves his realm to travel to the underworld, where he imprisoned his former lover Nada, to release her. Having previously departed the realm with it very angry with him (in the first collection, Preludes and Nocturnes), Morpheus is apprehensive about the task. He sets about it, wanting to do what is right, but prepared for a confrontation which he knows he may lose.
"I'm not blessed, or merciful. I'm just me. I've got a job to do, and I do it. Listen: even as we're talking, I'm there for old and young, innocent and guilty, those who die together and those who die alone. I'm in cars and boats and planes; in hospitals and forests and abbatoirs. For some folks death is a release, and for others death is an abomination, a terrible thing. But in the end, I'm there for all of them."
Death, talking about herself, in Dream Country.